1. Field of the Invention
The present invention relates to a heat storage system which comprises a phase change medium and a nucleating agent. More particularly, it relates to a regenerative device which comprises a gas hydrate as a phase change medium and a clathrate as a nucleating agent.
2. Description of the Prior Arts
Various substances beside ice have been studied as a phase change medium for cooling which utilizes heat of fusion, however only ice has been practically used. Tetradecane (C.sub.14 H.sub.30) has a melting point of 5.5.degree. C. and is expected to be usable as the phase change medium, however it is one of the paraffins where the thermal conductivity is only about 1/4 of that of water and a heat of fusion is only about 40 cal per unit volume.
Among clathrates of water which have dodecahedron structure as the basic crystalline form and have a melting point of 0.degree. to 10.degree. C., hydrate of trichlorofluoromethane (CCl.sub.3 F.17H.sub.2 O: melting point of 8.5.degree. C.) has been considered to be useful as the phase change medium for cooling. Melting points and heats of fusion of certain gas hydrates are shown in Table 1.
TABLE 1 ______________________________________ Melting point and heats of fusion of various gas hydrates Gas hydrate Melting Heat of Guest mole- point fusion cule Name Formula (.degree.C.) (Cal/g) ______________________________________ C.sub.2 H.sub.5 Cl ethyl chloride C.sub.2 H.sub.5 Cl . 17H.sub.2 O 4.8 69* CCl.sub.3 F trichloro- CCl.sub.3 F . 17H.sub.2 O 8.5 65* fluoro- methane** CHCl.sub.2 F dichloro- CHCl.sub.2 F . 17H.sub.2 O 8.7 64* fluoro- methane** C.sub.4 H.sub.8 O tetrahydro- C.sub.4 H.sub.8 O . 17H.sub.2 O 4.0 55 furan (CH.sub.3).sub.3 N trimethyl (CH.sub.3)101/4H.sub.2 O 5.2 41 amine ______________________________________ Note- *The heat of fusion of the guest molecule at converting into liquid. **Trichlorofluoromethane is referred as R11. Dichlorofluoromethane is referred as R21.
Ethyl chloride, R11 and R21 among the gas hydrates shown in Table 1 are respectively separated into two phases of the liquid guest molecule and water in the molten state, and accordingly, it is indispensable to stir them in the formation of a hydrate crystal. On the other hand, hydrates of tetrahydrofuran or trimethylamine respectively form each aqueous solution on their melting whereby it is not always necessary to stir them.
The problem for practically using these gas hydrates to impart the function as a phase change medium, is how to form nuclei and to form the gas hydrate crystal inside of the medium in a supercooling state. It has been desired to attain high reliability and high velocity. These gas hydrates, however, easily experience supercooling state thereby taking a long time for the nucleating (formation of nuclei).
It has been known that when a light gas such as CO.sub.2 is incorporated into the gas hydrate, it serves as a helping gas to facilitate the formation of nuclei. In this method, however, an autoclave is required which is not easy to use as it is a large size device. An antisupercooling agent for the gas hydrate has not been known.